wdiff draft-ietf-mpls-ldp-end-of-lib-00.txt draft-ietf-mpls-ldp-end-of-lib-01.txt

NetworkMPLS Working Group Rajiv Asati
Internet Draft Cisco Systems
Intended status: Standards Track
Expires: January March 2009 Pradosh Mohapatra
Cisco Systems

Bob Thomas
Cisco Systems

Emily Chen
Huawei Technologies

July 5,

September 15, 2008

LDP End-of-LIB
draft-ietf-mpls-ldp-end-of-lib-00.txt
draft-ietf-mpls-ldp-end-of-lib-01.txt

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Abstract

There are situations following LDP Label Distribution Protocol (LDP)
session establishment where it would be useful for an LDP speaker to
know when its peer has advertised all of its labels. These include session establishment
when LDP-IGP sync is in use, as well as session re-establishment
following loss of an LDP session when LDP graceful restart is in use. The LDP
specification [RFC5036] provides no mechanism for an LDP speaker to notify a
peer when it has completed its initial label advertisements to that
peer. This document specifies means for an LDP speaker to signal
completion of its initial label advertisements following session
establishment.

Conventions used in this document

In examples, "C:" and "S:" indicate lines sent by the client and
server respectively.

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].

Table of Contents

1. Introduction...................................................3 Introduction...................................................2
2. Specification Language.........................................3
3. Unrecognized Notification Capability...........................4 Capability...........................3
4. Signaling Completion of Label Advertisement....................4
5. Usage Guidelines...............................................5
5.1. IGP-Sync..................................................6 IGP-Sync..................................................5
5.2. LDP Graceful Restart......................................6
5.3. Wildcard Label Request....................................7
5.4. Missing Expected End-of-LIB Notifications.................7
6. Security Considerations........................................7
7. IANA Considerations............................................8 Considerations............................................7
8. Acknowledgments................................................8
9. References.....................................................9
9.1. Normative References......................................9
9.2. Informative References....................................9
Author's Addresses...............................................10
Intellectual Property Statement..................................10
Disclaimer of Validity...........................................11

1. Introduction

There are situations following LDP session establishment where it
would be useful for an LDP speaker to know when its peer has
advertised all of its labels. For example, when an LDP speaker is
using LDP-IGP synchronization procedures [LDPSync], it would be
useful for the speaker to know when its peer has completed
advertisement of its IP label bindings. Similarly, after an LDP
session is re-established when LDP Graceful Restart [RFC3478] is in
effect, it would be helpful for each peer to signal the other after
it has advertised all its label bindings.

The LDP specification [RFC5036] provides no mechanism for an LDP
speaker to notify a peer when it has completed its initial label
advertisements to that peer.

This document specifies use of a Notification message with the "End-
of-LIB" Status Code for an LDP speaker to signal completion of its
label advertisements following session establishment.

RFC5036 implicitly assumes that new Status Codes will be defined over
the course of time. However, it does not explicitly define the
behavior of an LDP speaker which does not understand the Status Code
in a Notification message. To avoid backward compatibility issues
this document specifies use of the LDP capability mechanism [LDPCap]
at session establishment time for informing a peer that an LDP
speaker is capable of handling a Notification message that carries an
unrecognized Status Code.

Copyright (C) The IETF Trust (2008). This version of this MIB module
is part of RFC XXXX; see the RFC itself for full legal notices.

2. Specification Language

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].

3. Unrecognized Notification Capability

An LDP speaker MAY include a Capability Parameter [LDPCap] in the
Initialization message to inform a peer that it ignores Notification
Messages that carry a Status TLV with a non-fatal Status Code unknown
to it.

The Capability Parameter for the Unrecognized Notification capability
is a TLV with the following format:

0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|U|F| Unrecog Notif (IANA) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S| Reserved |
+-+-+-+-+-+-+-+-+

Figure 1 Unrecognized Notification Capability format

Where:

U and F bits: Should be set 1 and 0 respectively as per section 4
of LDP Capabilities [LDPCap].

Unrecog Notif: TLV code point to be assigned by IANA.

S-bit: Must be 1 (indicates that capability is being advertised).

Upon receiving a Notification with an unrecognized Status Code an LDP
speaker MAY generate a console or system log message for trouble
shooting purposes.

4. Signaling Completion of Label Advertisement

An LDP speaker MAY signal completion of its label advertisements to a
peer by means of a Notification message, if its peer had advertised
the Unrecognized Notification capability during session
establishment. The LDP speaker MAY send the Notification message (per
FEC Type) to a peer even if the LDP speaker had no zero Label bindings
to
advertise. advertise to that peer.

Such a Notification message MUST carry:

- A status TLV with TLV E- and F-bits set to zero that carries an
"End-of-LIB" Status Code.

- A FEC TLV with the Typed Wildcard FEC Element [TypedWC] that
identifies the FEC type for which initial label advertisements
have been completed. In terms of Section 3.5.1 of RFC5036,
this TLV is an "Optional Parameter" of the Notification
message.

An LDP speaker MUST NOT send a Notification which carries a Status
TLV with the End-of-LIB Status Code to a peer unless the peer had
advertised the Unrecognized Notification capability during session
establishment.

This applies to both non-directed and directed any LDP peers. peers discovered via either basic discovery
or extended discovery mechanism (per section 2.4 of [RFC5036]).

5. Usage Guidelines

The FECs known to an LDP speaker and the labels the speaker has bound
to those FECs may change over the course of time. This makes
determining when an LDP speaker has advertised "all" of its label
bindings for a given FEC type an issue. Ultimately, this
determination is a judgement call the LDP speaker makes. The
following guidelines may be useful.

An LDP speaker is assumed to "know" a set of FECs. Depending on a
variety of criteria, such as:

- The label distribution control mode in use (Independent or
Ordered);

- The set of FEC's to which the speaker has bound local labels;

- Configuration settings which may constrain which label bindings
the speaker may advertise to peers;

the speaker can determine the set of bindings for a given FEC type
that it is permitted to advertise to a given peer.

IGP-Sync,

LDP-IGP Sync, LDP Graceful Restart, and the response to a Wildcard
Label Request [TypedWC] are situations that would benefit from End-of-LIB End-
of-LIB Notification. In these situations, after an LDP speaker
completes its label binding advertisements to a peer, it should send sending an End-
of-LIB Notification to the peer
an End-of-LIB Notification. makes their outcome deterministic.
The following subsections cover further explain each of these situations in turn.
one by one.

5.1. IGP-Sync LDP-IGP Sync is

The LDP-IGP Synchronization [LDPSync] specifies a mechanism by which
directly connected LDP speakers may use
to delay using the use of the link connecting them between
them, for transit IP traffic forwarding until the labels required to
support IP over MPLS traffic on the link forwarding have been
learned. distributed and
installed.

Without an End-of-LIB Notification Notification, the speaker must rely on some
heuristic to determine when it has received all of its peer's label
bindings. The heuristic chosen could cause LDP to signal the IGP too
soon in which case the likelihood that traffic will be dropped
increases, or too late in which case traffic is kept on sub-optimal
paths longer than necessary.

Following session establishment establishment, with a directly connected peer that
has advertised the Unrecognized Notification capability, an LDP
speaker using LDP-IGP Sync may send the peer an End-of-LIB
Notification after it completes advertisement of its IP label
bindings to the peer. Similarly, the LDP speaker may use the End-of-
LIB Notification received from a directly connected peer to determine
when the peer has completed advertisement of its label bindings for
IP prefixes. After receiving the notification, the LDP speaker
should consider LDP to be fully operational for the link and signal
the IGP to start advertising the link with normal cost.

5.2. LDP Graceful Restart

LDP Graceful Restart [RFC3478] helps to reduce the loss of MPLS
traffic caused by the restart of a router's LDP component. It
defines procedures that allow routers capable of preserving MPLS
forwarding state across the restart to continue forwarding MPLS
traffic for a pre-agreed upon
period using forwarding state installed prior to the restart.

During that period restart for a
configured time period.

The current behavior without End-of-LIB Notification is as follows:
the restarting router and its peers consider the preserved forwarding
state to be usable but stale until it is refreshed by receipt of new
label advertisements following re-
establishment re-establishment of new LDP sessions. sessions
or until the time period expires. When the time period elapses expires, any
remaining stale forwarding state is removed by the router.

Receipt of the

Receiving End-of-LIB Notification from a peer in an LDP Graceful
Restart scenario enables an LDP speaker to stop using stale
forwarding information learned from that peer and to recover the
resources it requires without having to wait until the timeout
occurs. time period
expiry. The time period expiry can still be used if the End-of-LIB-
Notification message is not received.

5.3. Wildcard Label Request

When an LDP speaker receives a Label Request message for a Typed
Wildcard FEC (e.g. a particular FEC element type) from a peer it
determines the set of bindings, it is permitted to advertise the peer
for the FEC type specified by the request. Assuming the peer had
advertised the Unrecognized Notification capability at session
initialization time, the speaker should send the peer an End-of-LIB
Notification for the FEC type when it completes advertisement of the
permitted bindings.

As in the previous applications, receipt of the Notification
eliminates uncertainty as to when the peer has completed its
advertisements of label bindings for the requested Wildcard FEC
Element Type.

5.4. Missing Expected End-of-LIB Notifications

There is no guarantee that an LDP speaker will receive End-of-LIB
Notifications from a peer even if the LDP speaker has signaled its
capability. Therefore, an implementation SHOULD NOT depend on the
receipt of such a Notification.

To deal with the possibility of missing notifications, an LDP speaker
may time out receipt of an expected End-of-LIB Notification, and if
the timeout occurs, it may behave as if it had received the
notification. If the End-of-LIB Notification message is received
after the time-out occurs, then the message should be ignored.

6. Security Considerations

No security considerations beyond those that apply to the base LDP
specification and described in [RFC5036] apply to signaling the End-
of-LIB condition as described in this document.

7. IANA Considerations

This draft introduces a new LDP Status Code and a new LDP Capability
both of which require IANA assignment.

8. Acknowledgments

The authors would like to thank Ina Minei, Alia Atlas, Yakov Rekhter Rekhter,
Loa Andersson and Luyuan Fang for their valuable feedback and
contribution.

This document was prepared using 2-Word-v2.0.template.dot.

9. References

9.1. Normative References

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.

[RFC5036] Andersson, L., Doolan, P., Feldman, N., Fredette, A. and
Thomas, B., "LDP Specification", RFC 5036, January 2001.

[LDPCap] Thomas, B., Aggarwal, S., Aggarwal, R., Le Roux, J.L., "LDP
Capabilities", draft-ietf-mpls-ldp-capabilities-02, Work in
Progress, May 2007.

[TypedWC] Thomas, B., Minei, I., "LDP Typed Wildcard FEC", draft-
ietf-mpls-ldp-typed-wildcard-03, Work in Progress, March
2008.

9.2. Informative References

[LDPSync] Jork, M., Atlas, A., Fang, L., "LDP IGP Synchronization",
draft-ietf-mpls-ldp-igp-sync-02, Work in Progress, June
2008.

[RFC3478] Leelanivas, M., Rekhter, Y., Aggarwal, R., "Graceful
Restart Mechanism for Label Distribution Protocol",
February 2003.

Author's Addresses

Rajiv Asati
Cisco Systems,
7025-6 Kit Creek Rd, RTP, NC, 27709-4987
Email: rajiva@cisco.com

Pradosh Mohapatra
Cisco Systems,
3750 Cisco Way, San Jose, CA, 95134
Email: pmohapat@cisco.com

Bob Thomas
Cisco Systems,
1414 Massachusetts Ave, Boxborough, MA, 01719
Email: rhthomas@cisco.com bobthomas@alum.mit.edu

Emily Chen
Huawei Technologies
No.5 Street, Shangdi Information, Haidian, Beijing, China
Email: chenying220@huawei.com

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